Many foods and beverage bottles have a large mouth and are sealed with a metal or composite closure. For example, sauces have traditionally been packaged in glass containers with an all metal closure. Other food products, such as jelly and beverages have been packaged in blow molded plastic bottles and sealed with composite closures. The food or beverage contents of large mouth, blow molded plastic bottles are often filled in a process in which the contents are at an elevated temperature at the time of filling, often over 180 degrees F., referred to as “hot-fill.” A closure is applied while the contents are hot to hermetically seal the container. The term “large mouth” as used in this disclosure is any container mouth having a closure size greater than 48 mm.
Composite closures typically include a metal disk for sealing the mouth of the container and a plastic skirt, which fits over the disk, for engaging the threads of the bottle. Composite closures are typically used for hot fill applications with plastic bottles because the metal disk provides a robust seal and good heat transfer among other benefits.
Single piece, all-metal closures are commercially available in several types. An all-metal, unitary screw-on closure has threads preformed in the skirt that correspond to the bottle threads. A ROPP (roll on pilfer proof) closure has threads formed during application of the closure to the bottle. Crown Cork & Seal, Inc. manufacturers an all-metal, 2-piece lugged closure under the trade name Orbit™. Another type of all-metal, unitary closure is a one-piece lugged closure having lugs formed on the bottom of the skirt to engage threads on a bottle neck.
Typically, lug closures are used only with either glass bottles or with plastic bottles in which the lug closure is applied as part of a cold filling process (that is, neither the contents nor the bottle is at an elevated temperature during filling). But lug closures are not often used with conventional hot-filled plastic bottles without crystallized neck finishes because of a particular problem. The hot-fill contents raise the temperature of the neck and finish of the bottle, which diminishes the hoop strength of the finish. Because lug closures only contact the finish at the lugs, the force of applying the lug closure to the finish distorts the shape of the finish. Because four lug closures are typical for closure sizes less than 77 mm, the problem is known as “squaring,” even though the term “squaring” is used herein for distortion by closures having other quantities of lugs. When the container cools, the squaring is set. The problem is especially prevalent in bottles having either a blow molded or injection molded finish when neither are crystallized as part of the container manufacturing process.